The pH of a 0.2 ~M aqueous solution of a weak monoprotic acid is 3 . What is the percentage ionisation of this acid?

Step-by-step solution

For a weak monoprotic acid, the hydrogen ion concentration is related to the pH by: [ H ⁺ ] = 10^ - pH Given pH = 3 , we have [ H ⁺ ] = 10⁻³ ~M . The relationship between [ H ⁺ ] , concentration C , and degree of ionisation is: [ H ⁺ ] = C Given C = 0.2 ~M : = [ H ⁺ ] C = 10⁻³ 0.2 = 5 10⁻³ = 0.005 Percentage ionisation = 100 = 0.005 100 = 0.5 % The distractor 0.005 % is incorrect because it represents the fractional degree of ionisation without converting it to a percentage. The distractor 5 % is the result of a de